Sulfonamide compounds (I) are a class of very important organosulfur compounds and are widely used in pesticide. For example, diclosulam (N-(2,6-dichlorophenyl)-5-ethoxy-7-fluoro-1,2,4-triazolo[1,5-c]pyrimidine-2-sulfamide) developed by Dow Agroscience Company is a triazolopyrimidine sulfamide high-potent herbicide (U.S. Pat. No. 5,163,995). Diclosulam is an acetolactate synthetase (ALS) inhibitor and can be rapidly absorbed by roots and stem leaves of weeds to achieve effects. Diclosulam is applied to pre-emergence treatment of planting soil in fields of crops such as soybeans and peanuts for controlling broadleaf weeds and is used for post-emergence control of broadleaf weeds in winter wheat fields.
Diclosulam can be prepared by condensing 2,6-dichloroaniline and triazolopyrimidine sulfonyl chloride. Since 2,6-dichloroaniline has extremely high steric hindrance, the condensation reaction between the 2,6-dichloroaniline and the triazolopyrimidine sulfonyl chloride is slow and the yield is low, resulting in low purity of a product. Although the reaction is improved in U.S. Pat. No. 5,973,148 and the reaction yield is increased, 3% of triazolopyrimidine sulfonic acid is still contained in the product. Due to its chemical and physical properties of diclosulam cannot be effectively refined through base-dissolving acid-crystallizing method. In addition, since diclosulam has low solubility in conventional solvents, it is difficult to be obtain high-purity diclosulam through a recrystallization method while taking the yield into account at the same time.
For other novel high-potent herbicides such as sulfentrazone (N-(2,4-dichloro-5-[4-difluoromethyl-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazole-1-yl]phenyl) methane sulfonamide, WO 8703782), cloransulam methyl (3-chloro-2-[(5-ethoxy-7-fluoro-1,2,4-triazolo[1,5-c]pyrimidine-2-yl)sulfonamide]methyl benzoate U.S. Pat. No. 5,163,995), florasulam (N-(2,6-difluorophenyl)-5-ethoxy-8-fluoro-1,2,4-triazolo[1,5-c]pyrimidine-2-sulfamide, U.S. Pat. No. 5,163,995), penoxsulam (2-(2,2-difluoroethoxy)-N-(5,8-dimethoxy-1,2,4-triazolo[1,5-c]pyrimidine-2-yl)-6-trifluoromethyl benzenesulfonamide, U.S. Pat. No. 5,858,924), flumetsulam (N-2,6-difluorophenyl)-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine-2-sulfamide, U.S. Pat. No. 4,910,306), pyroxsulam (N-(5,7-dimethoxy-1,2,4-triazolo[1,5-a]pyrimidine-2-yl)-2-methoxy-4-trifluoromethyl-3-pyridinesulfonamide, WO 2002036595), metosulam (N-(2,6-dichloro-3-methylphenyl)-5,7-dimethoxy-1,2,4-triazolo[1,5-a]pyrimidine-2-sulfamide, EP 0142152), etc., there exist similar technical problems due to similar chemical and physical properties.